The use of spin coating of polymers is widespread in the semiconductor industry. Generally, substrates are treated by applying a quantity of polymer to the top side of the wafer while the bottom side is adhered by vacuum to a rotatable vacuum chuck. The wafer is spun at a relatively high speed and excess polymer is spun off the wafer leaving a relatively thin film of polymer on the top of the wafer. After the substrate is coated it is necessary to heat the substrate to drive off most of the solvent part of the polymer formulation. This heating step is generally referred to as the Post Apply Bake (PAB). The substrate is then exposed to light generally at wavelengths equal to or less than 400 nanometers creating defined patterns that enable the building of the circuits that ultimately constitute the product and its function. Subsequent to the exposure and depending upon the chemical composition and type of polymer the substrate is once again heat treated in what is generally referred to as the Post Expose Bake (PEB). The substrate is then subjected to various chemistries depending again upon the chemical composition and type of polymer. After the develop step the substrates may again be heat treated in what is generally referred to as the Post Develop Bake (PDB). In the prior art the means of heating has been heated plates in individual chambers.
Recently it has become necessary that these photolithographic steps be carried out on reconstituted substrates or panels. The substrates have imbedded silicon devices generally with a matrix of plastic, which is most often epoxy. Owing to the instability of the plastic and the embedded silicon chips the substrates exhibit much warpage. As much as 10 millimeters of warpage on a 300 mm diameter substrate may occur. Because a hot plate heats by both radiation and natural convection and the substrate is not flat when heated on a hot plate, the temperature uniformity is not good. One solution is to suck the warped substrate flat on the plate, but this increases cost and complexity. As each hot plate is in its own chamber and the chamber must be accessed by a handling means, a door or cover member must be opened to each individual chamber, which not only occupies space but also increases cost and complexity. Furthermore, some of the heat treatment processes are lengthy necessitating a multiplicity of such hot plate chambers further increasing the overall cost and complexity of the machines performing the desired process.